As conventionally used bone regeneration materials, calcium phosphates, such as hydroxyapatite (HA), are known (see, for example, JP2010-273847A, JP2003-260124A, JP2009-132601A and JP2005-279078A).
In recent years, octacalcium phosphate (hereinafter referred to as “OCP”), which is a precursor of HA, has been found to have high action of promoting bone regeneration and high absorbability in vivo, compared with other calcium phosphates, such as HA and β-tricalcium phosphate (β-TCP) (see, for example, JP2006-167445A). Thus, OCP has particularly excellent properties as a bone regeneration material among calcium phosphates.
However, OCP, which is an inorganic substance, has poor shape-imparting properties. Therefore, applying OCP alone so as to, for example, regenerate an extensive bone defect region is difficult. In light of this difficulty, using a composite of OCP and collagen as a bone regeneration material has been proposed (see, for example, JP2006-167445A).
Clinical Implant Dentistry and Related Research, Vol. 13, No. 2, pages 112 to 123, 2011 and Tissue Engineering Part A, Vol. 20, Nos. 7 to 8, pages 1336 to 1341, 2014 disclose that a composite of OCP and collagen is useful as a bone regeneration material in dogs and humans, respectively. In the study of the composite of OCP and collagen as a bone regeneration material, only OCP particles having a particle size of 300 μm to 500 μm were used.
Tissue Engineering Part A, Vol., 15, No. 1, pages 23 to 32, 2009 discloses a comparison of an in vivo-implanted composite of OCP and collagen and an in vivo-implanted porous material consisting only of collagen in terms of bone regeneration. Tissue Engineering Part A, Vol., 15, No. 1, pages 23 to 32, 2009 discloses that a porous material consisting only of collagen does not bring about sufficient bone regeneration.